1. Field of the Invention
The present invention relates to an optical disk recording and reproducing apparatus recording a signal onto a disk using a laser from an optical pick-up, and reproducing a signal recorded on the disk using a laser.
2. Description of the Related Art
Disk players which read a signal from a disk using an optical pick-up are popular. In particular, optical disk recording and reproducing apparatuses capable of signal recording using a laser from an optical pick-up, as well as signal reproducing, have recently been introduced to the consumer market. Optical disk recording and reproducing apparatuses capable of signal recording onto a disk while controlling the disk to rotate at a high linear velocity, such as twice, four, six, eight, ten, and twelve times as fast as a standard linear velocity, are also being developed.
An optical disk recording and reproducing apparatus records signal onto a disk in response to a record command from a host device or a computer device. During this recording, a signal to be recorded onto a disk, or a recording signal, is temporarily stored in a buffer RAM and read therefrom to be recorded, so that the signal is recorded onto the disk.
In normal signal recording operation, writing of signals from the computer device into a buffer RAM, reading of signals from the buffer RAM, and recording of signals onto the disk are all carried out in accordance with the amount of signals to be recorded and signal recording condition. However, even though the signal recording onto the disk is carried out at a higher linear velocity during such normal signal recording operation, signal writing into the buffer RAM may not be carried out at a sufficiently high speed commensurate with that signal recording onto the disk. This may cause shortage of recording signals, and an interruption of signal recording onto the disk. This phenomena, generally referred to as buffer under-run, may be considered an error and may result in a critical error disabling signal reproduction from the disk.
In order to address these problems, techniques are suggested including one in which signal recording onto the disk is suspended upon occurrence of buffer under-run phenomena, and thereafter resumed when signals of a predetermined or more amount have been stored in the buffer RAM.
According to this technique, when the recording of suspended signal is resumed, a signal recorded onto the disk before the suspension is read from the disk, and another signal is recorded onto the disk so as to continue from that signal. For accurate resuming of once suspended signal recording, a reference signal derived from the disk and that for use in signal recording must be accurately synchronized to each other. This method is referred to as synchronization. A synchronization process is applied so as to synchronize a reference signal originated from the disk and that for use in recording a signal read from the buffer RAM. This process is achieved through forced control of the timing of the phase of the respective reference signals.
After the reference signals are synchronized to each other, a phase error component is added to a servo signal for control of the rotation of the spindle motor. Specifically, referring to FIG. 1, a gain is increased to a predetermined value at time T, or some time after the synchronization establishment, whereby a phase error component is added to a servo signal. The addition of a phase error component, however, may cause a problem including abrupt acceleration or deceleration of the spindle motor during a period before the spindle motor gets to normal servo operation. This hinders accurate resumption of once suspended signal recording.
In an optical disk recording and reproducing apparatus in which the disk is controlled to rotate at a constant linear velocity for signal recording, the disk actually rotates faster when a signal is to be recorded onto a part on the disk closer to the disk center rather than a part farther from the disk center. Conventionally, however, despite this difference in the disk rotation speed, a gain for addition of a phase error component to a servo signal is maintained constant wherever part on the disk a signal is to be recorded. This makes it impossible to achieve optimum speed control.
The present invention has been conceived to overcome the above problems and aims to provide a spindle motor control method adapted to an optical disk recording and reproducing apparatus which can solve the above problems.
According to the present invention, there is provided a spindle motor control method adapted to an optical disk recording and reproducing apparatus which reads a signal having been recorded onto a disk before the recording was suspended, and records another signal so as to continue from that signal read. In this spindle motor control method, a reference signal reproduced from the disk and that for use in signal recording are made synchronized to each other without utilizing a phase error component when resuming signal recording. Once synchronization is established, a phase error component is added to a servo signal of the spindle motor. With this arrangement, the rotation of the spindle motor can be accurately controlled when resuming the signal recording.
For addition of a phase error component, the gain of a phase error component is gradually increased while a phase error component is added to a servo signal. In this way, sharp acceleration or deceleration of the spindle motor can be prevented, so that continuity of signals being recorded onto the disk between before and after the resuming of the signal recording can be improved.
In particular, continuous increase of the gain enables gradual addition of a phase error component to a servo signal. This in turn enables controlling the spindle motor to rotate smoothly. Alternatively, stepwise increase of the gain can facilitate digital control of the gain.
The final level for a phase error component to reach as a result of gradual increase of its gain can be determined according to the location of a part on the disk at which to resume signal recording, making it is possible to control the rotation of the spindle motor irrespective of the location of a part on the disk at which to resume signal recording, specifically, whether the part is close to or far from the disk center.
The final level for a phase error component to reach as a result of gradual increase of its gain can also be determined according to the disk rotation speed, making it is possible to control the rotation of the spindle motor regardless of a recording speed even when an optical disk recording and reproducing apparatus capable of multiple speed recording is employed.